Can a cabled tach be Converted?

So I have a slight problem. A few friends and myself bought a junker bike to fix up and we've come to find that it's a 1981 XJ750R Seca engine stuck into a 1981 XJ650 Maxim body (we think, anyway).

The gauge cluster has a cabled tach coming out of the bottom but from everything I can find the 750 Seca engines had electronic tachs. Is there anyway to make this tach work without replacing the gauge cluster completely? I do not have any experience working with tachs so if anyone has any ideas I'm willing to learn and try anything.

Also, we're doing a Cafe Racer rebuild on this bike and so far it's coming along pretty well. I'll upload some pictures later because we'd enjoy any input we can get from you guys.

Thanks,
rubikscube2007

 

Sorry Rubik, you would have to replace the guts of the gauge to get it to work.

 

You can put an electronic tach on any XJ engine easily enough, but the other way around you're probably out of luck.

If you can get an electronic XJ tach, you may be able to swap the guts in order to keep the same cluster. Otherwise you might just want to look for an aftermarket tach/speedo/etc.

 

What do I need to do to attach the electronic tach to it?

 

You don't really need a tach because the engine is close to bulletproof anyhow.

And it would help to post-up the chassis VIN number.
and engine stamping #

8O

 

lol. We'd actually considered just leaving it but we figure we'll fix it anyhow, if anything for the education of doing it.

I think the VIN number is "4h7-106609".

And there's a stamp on the front of the engine: 748cm. Is that the engine stamp?

 

The steering neck has a white paper tag with a 17 digit #
The motor stamp is near the clutch cable end.
These numbers really help the Learned Ones here.

An electric tach can be spliced into the orange coil wire- - me thinks. . .

 

Okay, I pulled the correct VIN number: JYA4H7006BA106609

The motor stamp is: 15R-003438

 

Sure enough, as you thought, the VIN indicates a 1981 XJ650. And, as you've noted from the front casting numbers, the engine is a 750... not sure of the year, though.

 

Awesome. lol. Out of curiosity, since Google did me no good, do motorcycles need a tachometer to be legal in the United States?

If not, since it's a cafe racer mock up, how does everyone think a single hud with the speedo and odo in it would look? And does anyone know where to get a relatively cheap one?

 

You don't need a tach for inspection.
I think a single round pod would look great.
If you're going to trash the factory gauges you can buy aftermarket single round pods that have everything in one.
ie tach, speedo, nuetral, oil, highbeam.

 

The 15R-003438 engine is out of a 1982 XJ750J Maxim bike, the 3,337th one built that year.............

http://www.xjbikes.com/Forums/viewtopic/t=14577.html

The bike itself (1982 XJ650 Maxim) was the 6,508th one made that year exported to the USA.

 

Replacing the mechanical tach with an electronic one is pretty easy. I put a 750 engine in my 650 and had to do it. I found the proper gauge cluster on ebay. It just needs a wire added from the tach to one of the ignition coils and some rewiring inside the headlight bucket. I can get you details if you want.

 

Im with all the guys on this one. A simple tacho should short you out. Very easy to wire up, usually has 3 or 4 wires coming from it - acc, earth, coil and some will have a wire that will connect to the headlight relay so when you turn ur head lights on its internal light will come on.
I recommend a chrome 2" one would look great on the cafe racer. Most will come with some mounting brackets as well.

 

Where would I purchase one ?

 

Here are some ebay finds but really any local car and bike parts shops will have them


http://cgi.ebay.com/2inch-52mm-BLUE-DIG ... 7C294%3A50

 

My XJ700N would be hostile toward that tach gauge. She's normally very happy in the 6000-7000 range.

 

These guys carry some cool ones: http://www.jpcycles.com/groups.aspx?LID ... 61cea601f3 There's always JC Whitney: http://www.jcwhitney.com/Motorcycle-Gau ... 014720.jcw or Bike Bandit: http://www.bikebandit.com/search-produc ... ch=2&sc=10 or check THESE: http://egauges.com/cycle_gr.asp?Series= ... agod5QmcDg

 

This is for gitbox - I could do with that info. I HAVE AN 81 Maxim 650 came with a mechanical tac - not working. I have an elecrical one but no idea how to hook it up

 

hey gitbox, could i get those details about hooking up an elec tach? i have the same issue (650 frame 750 motor). you can pm me or post for everyone's benefit.

 

Well, the stock type ones take three wires:

Brown = +12V switched and fused (like from the gauge lights)
Black = Ground
Gray = tach input signal from either coil drive wire

The coils each have a two pin connector with one pin being 12V supply and the other pin going to a gray or orange wire that runs back to the TCI module. It's that gray or orange wire that the tach gets it's signal from.

Aftermarket tachs may connect up the same way, or may use an inductive pickup to get their input from one of the spark plug wires.

 

so one would have to wire brown to the coil, and black to the frame (?), and splice the gray into the coil to tci wire ?

 

No.

The brown wire should be connected to other brown wires, like from the gauge lights. The red/white at the coil does have 12V switched, but it's also got a LOT of switching noise from the coils.

Yes, the black would go to the frame, or to another black wire.

The gray would get spliced into either the gray or orange from the TCI box.